Fluid pump apparatus

ABSTRACT

A fluid pump utilizing a transducer excited elastic membrane. Resonant wave motion generated in the membrane serves as the fluid-pumping mechanism. Energy not used to produce fluid movement is extracted from the membrane by an output transducer and returned to the input transducer thereby creating unidirectional wave motion and insuring efficient operation.

O Unlted States Patent 1151 3,642,385 McMahon 1 Feb. 15, 1972 [54] FLUID PUMP APPARATUS 2,721,024 10/1955 Zeh ..230/55 2,761,392 9/1956 Parker ..103/53 [72] Mcmmm, Judy Farm 2,898,860 8/1959 Grober ..103/53 cafllsleiMass- 3,411,704 11/1968 Hilgert et a1. ..230/55 [22] Filed: Mar. 10, 1969 Primary Examiner-Wilham L. Freeh [21] Appl. N .2 80 Att0rney-J0hn E.Toupa1 s21 U.S.Cl. ..417/411 [57] ABS'RACT [51 Int. Cl ....F04b 43/00 A fluid pump utilizing a transducer excited elastic membrane. [58] Field of Search ..417/41 1, 413; 230/55; 103/53 R n Wave m i n generated in the membrane serves as the fluid-pumping mechanism. Energy not used to produce 56] References Cited fluid movement is extracted from the membrane by an output I transducer and returned to the input transducer thereby creat- UNITED STATES PATENTS ing unidirectional wave motion and insuring efficient operation. 1,978,866 10/1934 Konig ..230/55 2,686,280 8/1954 Strong et a1 ..230/55 25 Claims, 8 Drawing Figures /3-- w as ae l6 7 6. l5- ,ee -/8 34 /4 15 lea 18 PATENTEDFEB 15 I972 SHEET 2 F 4 a; M Z l5 1 1220 ize ulMolliziao -9 AM. 5T 1 l PAIENTEDFEMS I912 3.642.385

SHEET 4 UF 4 n 00 or Izweizior:

3,2 5. W 9 flit 02 22495 FLUID PUMP APPARATUS BACKGROUND OF THE INVENTION This invention relates generally to fluid pump apparatus, and especially relates to vacuum pump apparatus comprising a vibrating membrane as a pumping mechanism.

There exist many types of pumps for reducing system pressures to less than atmospheric. Because of certain individual and sometimes collective faults, none of these pumps is satisfactory for all vacuum pumping applications. For example, the various types of mechanical pumps and blowers are effective only in the low or intermediate vacuum range and for so called dirty" systems. Vapor pumps including both diffusion and ejector pumps cannot discharge directly to atmospheric pressure and, accordingly, entail the use of fore pumps and roughing pumps. Furthermore, the fluid-pumping mechanisms used in these pumps give rise to various problems including back streaming, back migration, back diffusion, limited ultimate pressure capabilities, etc. The various ion pumps including getter-ion and sputter-ion pumps typically require sorption type roughing pumps and, in addition, are susceptible to destructive arcing in response to sudden introduction of high pressure. Another undesirable trait of both vapor and ion pumps is a selective pumping characteristic that reduces or eliminates the ability to pump certain gases. This problem is particularly acute with respect to the pumping of vapor and typically entails the additional use of vapor traps disposed between the pump and the system being evacuated.

A relatively recently introduced commercial innovation is the turbine molecular pump that theoretically operates on a molecular drag principle and alleviates some of the problems described above. Besides a high manufacturing cost, presently available turbine molecular pumps have the disadvantage of being unable to pump from ultra high vacuum directly to atmosphere. Furthermore, achieving such performance with a turbine molecular pump is beyond the practical limits of available material properties because failure of moving components may give rise to dangerous high-velocity projectiles.

The object of this invention, therefore, is to provide an improved vacuum pump that eliminates many of the deficiencies associated with previously used and known vacuum pumps.

SUMMARY OF THE INVENTION In accord with the well known theory of vibrating membranes, a traveling wave motion may be induced in a membrane under tension. The speed of the wave is determined by the tension on the membrane and the physical properties of the membrane material. The composite shape and direction of motion of the wave result from the boundary conditions around the area of the membrane allowed free movement. According to a preferred pump embodiment of the present invention tension is applied across a rectangular membrane such that a wave motion, mechanically generated at one end, will propagate to the opposite end. The membrane is enclosed, except at the ends, by solid material to form a cavity in which the walls are made precisely identical to the envelope of the membrane wave. This arrangement is analogous to that of a piston in a cylinder, in the respect that, the motion of the membrane wave within the cavity causes the gas to flow ahead of it.

In order to attain unidirectional wave motion, and eliminate end reflection which results in a standing wave, it is essential that the output end of the membrane be coupled to a means of extracting the energy of the wave from the membrane. The pump herein disclosed accomplishes this with a transducer, mechanically coupled to the output end of the membrane, which transforms the mechanical energy of the advancing wave to electrical. A similar transducer drives the input end of the membrane, transforming electrical energy to mechanical. Separation between the points on the membrane to which the transducers are coupled is measured in one-half wavelength multiples of the membrane wavelength to obtain an in phase relationship between the motion of the input and output transducers. One and one-half wavelengths is the preferred separation.

The fundamental operating principle of the invention is inherent in the means of returning electrical energy from the output transducer to the input transducer so as to achieve a circulating energy flywheel effect, to replace energy dissipated in the process of circulating, and to ensure unambiguous direction of wave motion. This means also provides the output transducer with the constant load impedance necessary to prevent wave reflection throughout the extent of variable pressure differential loads encountered during operation.

With selection of a membrane material such as spring steel, wave velocities comparable in magnitude to molecular velocities and wave power levels in the kilowatt range can be achieved. These wave velocities, well above meters per second, permit the device to function as an ultrafast molecular pump with the advantage of a positive seal separating successive volumes of pumped gas.

Pumping action in the molecular region of pressure requires very little energy expenditure because the actual quantity of transferred matter in the gas pumped is minute. In contrast, pumps currently used in the viscous region of pressure transfer relatively large quantities of matter and require relatively high power to do so. Since only a portion of the power circulating through a membrane of the instant pump can be applied directly to pumping gas, it is clear that high wave power is desirable. The fact that sufficiently high power is indeed available in the pump, as a consequence of its novel structure, directly leads to the additional capability of practical operation in the viscous region of pressure.

According to additional features of the invention input and output valves are located at the corresponding ends of the membrane cavity. The output valve functions efficiently at cycling rates of several hundred operations per second and prevents back leakage of gas from the higher pressure level into the pump cavity when the pressure inside is lower.

The input valve is constructed to limit input conductance of gas into the cavity while the pump is operating from zero pressure differential to a pumpdown volume pressure around half ambient, below which, this valve is normally fully open. Its purpose is to confine demand upon the electrical power supply circuit close to that required for operation throughout the remainder of the pressure range. Pumpdown time of a given volume is increased by a few percent, but required power supply capacity is considerably reduced.

DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic perspective view of a preferred pump embodiment of the invention;

FIG. 2 is a partial cross-sectional view of the pump shown in FIG. 1;

FIG. 3 is a partial, cross-sectional perspective view of a preferred outlet valve for the pump shown in FIG. 1;

FIGS. 4-6 are partial, cross-sectional perspective views showing in three different operating positions the inlet valve for the pump shown in FIG. 1;

FIG. 7 is a schematic circuit diagram of a power supplyfor the pump embodiment shown in FIG. 1; and

FIG. 8 is a partial, cross-sectional perspective view of another preferred outlet valve embodiment for use with the pump shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically illustrates in perspective a preferred embodiment of the invention including the rectangular pump housing 10. At one end of the housing 10 is the outlet 10a and at the opposite end an inlet defined by the flange 10b adapted for attachment to the mating flange (not shown) of a chamber to be evacuated. Mounted on each sidewall 12 of the housing 10 is a pair of electrical transducers 11 and 11a, one disposed adjacent the inlet flange 10b and the other adjacent the outlet a. Preferably the pump 10 is made symmetrical from side to side as shown in order to cancel any spurious vibration due to the reciprocating movement of transducer components as described below.

FIG. 2 is a cross-sectional view in elevation of the pump housing 10 taken in a plane passing through the axis of one of the cylindrical transducers 11, all of which are identical. Only slightly more than half of the pump 10 is shown in FIG. 2 it being understood that the remaining half is identical to that shown. The pump housing 10 includes the plurality of elongated rectangular internal plates 13. These plates extend through the full length of the pump and have shaped surfaces 14 that form the pump chambers 15. Straddled by the identical pump halves encompassing the chambers 15 is the central cavity 16 divided into separate sections by the longitudinally disposed plates 16a.

Included in the transducer 11 is the permanent magnet 22 and the concentric wire coil 23 retained by the annular shell 23a. The wire coil 23 and shell 23a, which move in reciprocating fashion in response to alternating voltage across the coil, is coupled through a shaft 24 to four of the membranes 25. In addition, the coil shell 23a is mechanically coupled to the pumps sidewall 12 through a heavy spring 26, which is designed to resonate the moving parts of the assembly at the operating frequency of the pump and to conduct away heat dissipated by the electrical current flowing in the coil 23 (the principal factor governing maximum operating power of the pump).

The membranes 25 are rectangular and extend through the full lengths of the pumping chambers 15. Preferably, the chamber walls 14 conform to the envelope of the membrane's 25 resonant motion produced by appropriate energization of the coil 23. Also illustrated in FIG. 2 is an arrangement for inducing tension across the membranes 25. A top bar 27 retained within recesses in the internal plates 13, and a bottom bar 28, both having the same length as the membranes 25', are welded or otherwise attached to each membrane 25. Bolts 29 are located along the lengths of the top bar 27 upon which nuts 19 are fastened and uniformly tightened, initially to a designated torque wrench reading, then to a final setting determined by transducer voltages as described below.

Pressure isolation of the transducer assembly 11 from the pump interior is accomplished by means of a flexible metal diaphragm 18. The diaphragm 18 and membranes 25 are clamped between hollow cylindrical spacers 17 mounted on and concentric with the coupling shaft 24.

FIG. 3 illustrates a preferred output valve embodiment viewed from a cross section cut across two pump chambers 15 near vertical center and looking up the outside surface at the output end 10a of the pump housing 10. The illustrated embodiment basically comprises differential pressure valves 33 constructed to permit independent flow from either outside edge of a pump chamber 15 when the pressure inside the chamber, caused by movement of the membrane 25, exceeds the outside pressure.

Each valve 33 is made of a semiflexible material (for example, a silicone-based plastic) shaped to cover the end of a chamber 15. Two narrow wedges or flaps of the material extend slightly beyond each outside edge of the chamber 15. One flap at the side of each valve 33 is shown raised as when gas is expelled from the chamber interior, while the flap at the opposite side of each valve 33 is shown closed. The semiflexible material is supported by a metal frame 34 against distension due to differential pressure loading across the valve. This valve is capable of minimizing space between the inside surfaces of the valve 33 and the adjacent edges of the membranes 25 to provide a virtual seal between the volumes within the chambers 15 separated by the membranes 25. An additional feature of thisembodiment, a consequence of the valve's tapered edges, is the capacity to accommodate an almost arbitrary range of irregular gas flow conditions without motional resonance tending to favor some one condition, or set of conditions, over others.

A preferred input valve embodiment is shown in FIGS. 4-6. The assembly is viewed from a cross section cut from side to side through the centers of the pump chambers 15 and looking up the outside surface at the input end 10b of the pump housing 10. In the interest of clarity, the shafts which couple the input transducers to the membranes 25 are omitted. An outer plate 41 and inner plate 42, having apertures conforming to the input openings of the cavities 15, are able to slide in opposite directions when the valve is actuated. The force applied to moving the aperture plates originates from a flexible metal diaphragm 45 which is distended by a difi'erence in pressure between the internal cavity 16 and the pumpdown volume (not shown) connected to the pump 10 by the inlet flange 10b. Movement is transmitted from the diaphragm 45 through the shaft 46, connected to the center of the diaphragm, to the levers 47 and finally to the notched sockets 48, which are an integral part of the aperture plates 41 and 42. As shown, the levers 47 are operatively connected to'the'shaft 46 at pivot points 47a and to the fulcrum posts 43 and 44. The stop arm 49 attached to one of the posts 44 arrests valve movement at the point where the input valve is fully open.

FIG. 4 shows the input valve very slightly open as would occurin response to a small differential pressure across the diaphragm 45. FIG. 5 shows the input valve half open indicating an intermediate value of differential pressure and FIG. 6 shows the input valve fully open which results from a large differential pressure. Thus, the input conductance to the pump 10 is rendered low at the start of pumpdown when differential pressure across the diaphragm 45 is small and is caused to increase automatically to its maximum value as pumpdown progresses.

An alternate method of limiting the quantity of gas pumped, and therefore the power drawn from the supply, obviates the need for an input valve to limit input conductance. This method consists of controlling the input transducer voltage to vary the wave amplitudes of the membranes 25. Since pumpdown volume pressure is the desired control variable, a device (not shown) such as a thermocouple pressure gauge or diaphragm actuated linear potentiometer can be used to convert pumpdown volume pressure to. a corresponding electrical signal. Applying this electrical signal to control of the input transducer voltage is easily accomplished using conventional servomechanism design theory to devise an appropriate electrical circuit. This approach to limiting power drawn by the pump from its power supply is deemed sufficiently obvious to anyone versed in the art not to require further elaboration.

According to the preferred method of pump operation, unidirectional wave motion is produced along the membranes 25. The simplest circuit arrangement for producing this unidirectional membrane wave motion is to connect a resistive load across the coils of each output transducer 11a. The correct value of this load resistance is equal to the membrane characteristic impedance reflected through the transducer. Then all energy transmitted along the membranes 25 in the membrane waves is absorbed by the resistive loads. In such an arrangement the loss of energy by the membrane wave while in transit between an input transducer 11 and an output transducer 1 la results in a decrease of voltage generated at the output transducer 11a below the constant voltage applied to the input transducer 11. The reason for this is evident in the fact that output power generated by the membrane 25 at the output transducer 11a is less than power coupled into the membrane 25 at the input transducer 11 by the amount of power lost in transit. Stated explicitly: the r.m.s. voltage across the coil of the output transducer 11a is equal to the square root of the product of output power and load resistance. It follows that, power loss during transmission of the wave along the membrane 25 gives rise to a corresponding voltage difference between the input and output transducers 11 and 11a.

However, the described basic circuit isnt very desirable because of its inefficiency. Power dissipated in the resistive load serves no useful purpose, and the amount of power lost in this manner is significantly greater than the power utilized by the membranes 25 to pump gas. Thus, the first essential of a more practical circuit arrangement is a method of returning unused power generated at an output transducer 11a back to an input transducer 11. Also any modified circuit arrangement should be capable of reproducing, for the same power loss, the same transducer voltages and currents produced by the basic circuit described above as these conditions ensure the desired unidirectional wave motion.

Since the characteristic impedance of the membrance 25 reflected at the input transducer 11 is identical to that at the output transducer 11a, an idealized situation characterized by zero power loss would permit connection of the output transducer coil directly across the input transducer coil. In this instance, a power generator (not shown) also connected across the input transducer and operating at the same voltage as normally appears at the input transducer would supply no net cur rent, and therefore no power, to the input transducer. However, when power loss is introduced, the voltages across the input and output transducers will not be identical and a direct connection must lead to incorrect circuit operation. Thus, establishment of desired operation requires connection of a voltage source between the two transducers. The voltage source must be equal in magnitude to the voltage difference of the input and output transducers as determined by the basic circuit. With this new arrangement, current generated at the output transducer is returned to the input transducer, and the current supplied by the power generator to the input transducer is reduced by the amount of the output transducer current returned. Also, the amount of current supplied by the power generator to the input transducer is directly proportional to the correct voltage of the voltage source connected between the input and output transducers. This relationship is the basis for design of a practical power supply circuit.

FIG. 7 is a circuit schematic of a preferred power supply embodiment based on the above described circuit analysis. The input transducer 11 is driven directly by the alternating current power source 52 via the source transformer 53, which converts the source voltage to the amplitude at which the input transducer operates. The winding 61 of the source transformer 53 connected across the input transducer coil 23 is equivalent to the power generator referred to previously. In series with the same winding of the source transformer 53 is the current transformer 59, connected at the input of a pushpull amplifier 60. This amplifier 60 provides an output 55, connected between the input transducer 11 and the output transducer lla, which is proportional to the current supplied by the source transformer 53 to the input transducer 11. In practice only one power supply would be used for the pump with all input transducers 11 connected in parallel and all output transducers lla connected in parallel. The amplifier output 55 is equivalent to the voltage source referred to previously. Evidently, the total power drawn by the pump is equal to the current-voltage product at the amplifier output 55 plus the current-voltage product at the secondary winding 61 of the source transformer 53.

The low amplifier output impedance characteristic of a voltage source, and relative independence from circuit component variations are obtained by means of the negative feedback connection from a winding 57 on the amplifier output transformer 62 to a winding 63 of the current transformer 59 at the amplifier input. Minor adjustment of gain is made with the variable resistor 56.

For operation the amplifier gain may be properly adjusted by temporarily disconnecting the output 55 from the output transducer lla, connecting a resistive load (not shown) across the output transducer lla equivalent to the reflected membrane characteristic resistance, and setting the gain with resistor 56 so that the amplifier output voltage 55 matches the voltage across the input transducer coil 23 in response to alternating current applied to the input transducer. With preliminary adjustment in this manner, and the circuit connections restored to normal, initial application of power at turn on of the supply 52 will give rise to the following conditions: (I)

the input transducer 11 is set into an oscillatory-motion of amplitude determined by the amplitude of the applied alternating voltage. (2) the current supplied to the input transducer coil 23 at start up will cause a voltage at the amplifier output 55 equal to the voltage across the input transducer 11, with the result that no voltage is applied to the output transducer 11a. (3) the motion of the membranes 25 coupled to the input transducer 11 will be transmitted along the membranes in the form of a wave. (4) when the membrane wave reaches the point where the output transducer lla is coupled to the membrane 25, the output transducer will be set into motion and generate a current. Since this current must flow through the amplifier output winding 64 and also through the input transducer coil 23, the power source current needed to sustain the proper voltage across the input transducer coil 23 is correspondingly reduced. Equilibrium is reached when the operating losses in the system are just compensated for by power supplied from the electrical circuit.

The preceding steps indicate how unidirectional membrane wave motion is initiated upon application of power to the system. Furthermore, once begun, unidirectional wave motion is sustained by the action of the illustrated power supply circuitry, which constrains transducer voltages and currents to the same conditions defined by the above-described but not shown open-loop circuit.

FIG. 8 is a partial view of another preferred output valve embodiment shown in the same manner as the output valve of FIG. 3. Wedge-shaped plugs 75, of low-density material, are held in place by light springs 76. Two plugs 75 are allocated to each pump chamber 15 placed, as indicated, at the outside edges of the chambers 15. One plug 75 at each chamber is shown raised as when gas is expelled from the same side of that chamber, while the other plug 75 is shown closed. Gas is vented independently from each of the two volumes within the pump chambers 15 separated by the membranes 25, and also, minimal separation between the edge of a membrane 25 and the inside surface of the valve seat plate 77 remains practicable.

In preferred embodiments of the invention certain structural relationships are utilized to optimize performance. The existence of these relationships is most easily demonstrated by mathematical analysis. Of course, many of the following expressions are simplified to facilitate their use. The approximations generally provide results accurate to within a few percent.

The wave velocity is related to the membrane parameters as follows:

where,

v wave velocity (meters per second) T= static membrane tension (Newtons per square meter) Y= Youngs modulus of membrane material (Newtons per square meter) z maximum membrane displacement normal to zero displacement plane (meters) L wavelength of membrane wave (meters) D= density of membrane material (kilograms per cubic meter) f= operating frequency of pump (herz) The condition that the elastic limit, M (newtons per square meter), of the membrane material is not exceeded is:

T-l-6l (2/L) s M Finally, to ensure that effects of higher harmonics resulting from nonlinear membrane tension are kept small, the additional condition is imposed:

6l(z/L) s T giving, if equality is assumed:

T=0.5D(fL) To achieve the desired resonant wave condition, the preferred dimensions of the active area of the membrane are L/2 for the width and 3L/2 The membrane wave propagates along the larger dimension.

Effects due to membrane stiffness are neglected in the above expressions since, if the effects are small, they may easily be compensated for by slightly decreasing the static tension, 7, on the membrane.

Next, operation in the viscous region of pressure is considered. Clearly, the process of pumping gas involves a transfer of energy from the membrane wave to the gas and must result in a decrease in amplitude of the wave as it advances from the input transducer to the output transducer. Since the dimensions of the cavity are fixed, the decrease in membrane wave amplitude causes a slight opening between the peak of the membrane wave and the cavity wall. Consequently, during a compression cycle, some portion of a gas is leaking or escaping out of the compression volume back towards the input end of the pump. The following expressions (trigonometric arguments are given in radians) take this circumstance into account:

where,

J a parameter determined by assigning to it incremental values from to l and, using the appropriate equation, plotting the ratio P /P against the assigned values. Then J is defined by the plot for any given ratio P /P.

ambient pressure (approx. l.0l3 l0 Newtons per square meter) P, initial pressure of compression volume at start of compression cycle. When the input valve is fully open, this pressure is approximately the same as the pumpdown volume pressure (Newtons per square meter) g specific heat ratio ofgas pumped (approx. 1.4 for air) I time during an individual pump cycle, having a value falling between zero and l/f. The product,ft, refers to the fraction of the cycle time at which the maximum compression pressure has been reached. (seconds) G constant relating back leakage of gas to pump dimensions (meters to the fifth power divided by Newton-sec.)

A loss coefficient of energy transmitted by membrane wave to gas l/meters) P, pressure of pumpdown volume (Newtons per square meter) V,, mean molecular velocity of pumped gas (approximately 470 meters per second for air) W= power transmitted along membrane by wave (watts) S, estimated pumping speed in viscous region referred to pumpdown volume (cubic meters per second) The result of limiting input conductance of the pump with the input valve shown in FIGS. 4-6 is a decrease in the value of P below P,, and therefore, a reduction of pump speed corresponding to less power drawn from the supply. In the expression for S,., the factor L2 is introduced to represent spurious energy loss from the 'pump in the form of heat and energy loss resulting from operation of the output valves. The assumption is made that this loss can be equated to a lossless pump operating into an ambient pressure 1.2 times higher than the actual condition.

Thus, the invention provides a pump that offers a combination of advantages not present in any prior vacuum pumps. Because the pump requires no fluid in its operation, back diffusion and a minimum pressure limitation due to the vapor pressure of a working fluid are eliminated. The pump cannot be damaged by a sudden introduction of high pressure such as would cream" a diffusion pump, or cause destructive arcing in an ion pump. For this reason, and because of neglegible parts wear, a long operating life without maintenance can be achieved. Positive pumping action renders the pump independent of individual gas characteristics. Operation of the pump is independent of both orientation and changing orientation. The pumps may be designed in sizes covering almost every conceivable application, from hand-carried portable instruments to million cubic feet space simulation chambers for which relatively short pumpdown time to ultrahigh vacuum pressures is desired. Also the pumps capability to pump vapors, and eliminate vapor traps, is a consequence of the fast cycling rate and the corresponding extremely fast rate of pressure change.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example only, tandem combinations of pumps may be utilized to realize special application objectives such as extra-high reliability through redundancy, uniform pumpdown time in the situation of a variable pumpdown volume, or modification of the immediately available speed vs. pressure curve. Also, power supplies more sophisticated than that shown may be desirable for certain applications.

What is claimed is:

l. A fluid pump apparatus comprising a pump housing that defines fluid inlet and fluid outlet ports, elastic membrane means supported by said housing and adapted to sustain resonant traveling wave motion propagating in a direction between said inlet and outlet ports, input transducer means coupled to 'said membrane means and adapted to induce travelingwave motion therein, and output transducer means coupled to said membrane means and adapted to extract therefrom wave energy introduced therein by said input transducer means.

2. A fluid pump according to claim 1 including energy transmission means coupled between said input and output transducer means and adapted to transmit to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.

3. A fluid pump according to claim 2 wherein said membrane means is enclosed by said pump housing.

4. A fluid pump according to claim 3 wherein said pump housing comprises sidewalls that conform to the envelope of the transverse traveling wave resonant motion of said membrane means.

5. A fluid pump according to claim 4 including an output impedance means matched to the characteristic mechanical impedance of said membrane means.

6. A fluid pump according to claim 1 including an output impedance means matched to the characteristic mechanical impedance of said membrane means.

7. A fluid pump according to claim 6 including energy transmission means coupled between said input and output transducer means and adapted to transmit to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.

8. A fluid pump according to claim 1 wherein said input transducer means is adapted to convert electrical energy into mechanical energy and said output transducer means is adapted to convert mechanical energy into electrical energy.

9. A fluid pump according to claim 8 wherein said input transducer means is adapted to convert electrical energy into reciprocating linear motion.

10. A fluid pump according to claim 9 wherein said input transducer means is mechanically resonant at the resonant frequency of said membrane means.

11. A fluid pump according to claim 10 including electrical circuit means adapted to return to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.

12. A fluid pump according to claim 11 wherein said electrical circuit means comprises an output impedance connected to said output transducer means and matched to the characteristic mechanical impedance of said membrane means.

13. A fluid pump according to claim 12 wherein said electrical circuit means further comprises a power amplifier adapted to convert current supplied to said input transducer means into a voltage applied between said input and output transducer rneans.

14. A fluid pump according to claim 13 wherein said membrane means is enclosed by said pump housing.

15. A fluid pump according to claim 14 wherein said pump housing comprises sidewalls that conform to the envelope of the transverse resonant motion of said membrane means.

16. A fluid pump according to claim 15 including an adjustable control means adapted to provide a variable conductance through said inlet port.

17. A fluid pump according to claim 16 including pressure responsive regulation means for regulating said adjustable control means in response to changes in the pressure within a volume in fluid communication with the interior of said pump housing via said inlet port.

18. A fluid pumpaccording to claim 17 including pressure responsive outlet valve means adapted to automatically open and close said outlet port in response to variations in the pressure differential produced across said outlet valve by the wave motion of said membrane means.

19. A fluid pump according to claim 8 including electrical circuit means adapted to return to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.

20. A fluid pump according to claim 19 wherein said electrical circuit means comprises an output impedance connected to said output transducer means and matched to the characteristic mechanical impedance of said membrane means.

21. A fluid pump according to claim 20 wherein said electrical circuit means further comprises a power amplifier adapted to convert current supplied to said input transducer means into a voltage applied between said input and output transducer means.

22. A fluid pump according to claim 8 wherein said membrane means is enclosed by said pump housing.

23. A fluid pump according to claim 22 wherein said pump housingcomprises sidewalls that conform to the envelope of the transverse resonant motion of said membrane means.

24. A fluid pump apparatus according to claim 6 including power supply means coupled to said input transducer means and adapted to produce resonant unidirectional wave motion of said membrane means from said input transducer means toward said output transducer means.

25. A fluid pump apparatus according to claim 24 wherein said membrane means comprises an active portion that is rectangular and has a length in the direction of wave motion substantially equal to 3L/3 and a width substantially equal to L/2 where L is the wavelength of the wave motion generated in said membrane.

I UNITED STATES PATENT OFFICE] CERTIFICATE OF" CORRECTION Patent NO. 3,642,385 -w February 15,197

Iriventor(s) v Eiigene A. McMahon 1 I (It is certified that error 'a 'pea'rs it; theebov ei d ent i fied p atent andthat said Letters Patent are-:hereby corrected as shown below:

Column 6, line 50, change to Column 7, li ne 2 5, change '3 /-8 v Si e-ed and sealed this 5th day of September 1972.

Attest: I

ummw l-'I.FLi5ISHEH, JR ROBERT GO TTSGHA LK Attesting Officer v v Commissionerof Patents USCOMM-DC GOING-P69 u.s. GOVERNMENT PRINTING OFFICE: I969 0-366-334 FORM PO-1050 (10-69) 

1. A fluid pump apparatus comprising a pump housing that defines fluid inlet and fluid outlet ports, elastic membrane means supported by said housing and adapted to sustain resonant traveling wave motion propagating in a direction between said inlet and outlet ports, input transducer means coupled to said membrane means and adapted to induce traveling wave motion therein, and output transducer means coupled to said membrane means and adapted to extract therefrom wave energy introduced therein by said input transducer means.
 2. A fluid pump according to claim 1 including energy transmission means coupled between said input and output transducer means and adapted to transmit to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.
 3. A fluid pump according to claim 2 wherein said membrane means is enclosed by said pump housing.
 4. A fluid pump according to claim 3 wherein said pump housing comprises sidewalls that conform to the envelope of the transverse traveling wave resonant motion of said membrane means.
 5. A fluid pump according to claim 4 including an output impedance means matched to the characteristic mechanical impedance of said membrane means.
 6. A fluid pump according to claim 1 including an output impedance means matched to the characteristic mechanical impedance of said membrane means.
 7. A fluid pump according to claim 6 including energy transmission means coupled between said input and output transducer means and adapted to transmit to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.
 8. A fluid pump according to claim 1 wherein said input transducer means is adapted to convert electrical energy into mechanical energy and said output transducer means is adapted to convert mechanical energy into electrical energy.
 9. A fluid pump according to claim 8 wherein said input transducer means is adapted to convert electrical energy into reciprocating linear motion.
 10. A fluid pump according to claim 9 wherein said input transducer means is mechanically resonant at the resonant frequency of said membrane means.
 11. A fluid pump according to claim 10 including electrical circuit means adapted to return to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.
 12. A fluid pump according to claim 11 wherein said electrical circuit means comprises an output impedance connected to said output transducer means and matched to the characteristic mechanical impedance of said membrane means.
 13. A fluid pump according to claim 12 wherein said electrical circuit means further comprises a power amplifier adapted to convert current supplied to said input transducer means into a voltage applied between said input and output transducer means.
 14. A fluid pump according to claim 13 wherein said membrane means is enclosed by said pump housing.
 15. A fluid pump according to claim 14 wherein said pump housing comprises sidewalls that conform to the envelope of the transverse resonant motion of said membrane means.
 16. A fluid pump according to claim 15 including an adjustable control means adapted to provide a variable conductance through said inlet port.
 17. A fluid pump according to claim 16 including pressure responsive regulation means for regulating said adjustable control means in response to changes in the pressure within a volume in fluid communication with the interior of said pump housing via said inlet port.
 18. A fluid pump according to claim 17 including pressure responsive outlet valve means adapted to automatically open and close said outlet port in response to variations in the pressure differential produced across said outlet valve by the wave motion of said membrane means.
 19. A fluid pump according to claim 8 including electrical circuit means adapted to return to said input transducer means substantially all of the energy extracted from said membrane means by said output transducer means.
 20. A fluid pump according to claim 19 wherein said electrical circuit means comprises an output impedance connected to said output transducer means and matched to the characteristic mechanical impedance of said membrane means.
 21. A fluid pump according to claim 20 wherein said electrical circuit means further comprises a power amplifier adapted to convert current supplied to said input transducer means into a voltage applied between said input and output transducer means.
 22. A fluid pump according to claim 8 wherein said membrane means is enclosed by said pump housing.
 23. A fluid pump according to claim 22 wherein said pump housing comprises sidewalls that conform to the envelope of the transverse resonant motion of said membrane means.
 24. A fluid pump apparatus according to claim 6 including power supply means coupled to said input transducer means and adapted to produce resonant unidirectional wave motion of said membrane means from said input transducer means toward said output transducer means.
 25. A fluid pump apparatus according to claim 24 wherein said membrane means comprises an active portion that is rectanguLar and has a length in the direction of wave motion substantially equal to 3L/3 and a width substantially equal to L/2 where L is the wavelength of the wave motion generated in said membrane. 